Rafael Nadal of Spain celebrates his win against Juan Martin del Potro of Argentina.
REUTERS/Mike SegarMELBOURNE, Jan 22 (Reuters) - Rafa Nadal kept the flag flying for the old guard at the Australian Open with a 6-3 6-4 6-2 win over American Frances Tiafoe on Tuesday for a place in the semi-final, where he will meet another next generation player in Stefanos Tsitsipas.Nadal's match against Tiafoe, who turned 21 on Sunday, was billed as an intriguing clash of generations after the loss of Roger Federer to Tsitsipas earlier, but the second seed was ruthless as he reached the last four without dropping a set.The 17-time Grand Slam champion broke Tiafoe's first service game in each set and with a second break in the third set wrapped up the victory in an hour and 47 minutes.For a place in the final, Nadal will meet 20-year-old Greek sensation Tsitsipas, who earlier on Tuesday became his country's first player to reach the last four at a major with a 7-5 4-6 6-4 7-6(2) triumph over Spaniard Roberto Bautista Agut.